This invention relates to processes for the manufacture of plastic pirn sleeves having rows of indentations in the external surface of thermoplastic tubing.
Indentations in the external surface of thermoplastic tubing are required in various applications for utilitarian and for decorative purposes. One such application is in the production of plastic sleeves for textile bobbins or pirns. The indentations can take the form of circumferential grooves arranged in rows, parallel to the axis, with intervening axial blank areas. These grooves and their associated "teeth", however, have ends which are raised above the surface of the intervening axial blanks. These exposed ends, unfortunately, can be ragged and entangle fine filaments jeopardizing smooth payout of filaments on high speed unwinding. It is the purpose of this invention to provide a novel plastic pirn sleeve having the ends of grooves and "teeth" substantially flush at the juncture with the intervening axial blank areas. It is a further purpose to provide pirn sleeves that allow a smoother yarn take-off tension which can be varied by varying the width and number of grooves rows. It is a further purpose to provide a non-entangling flush-end grooved pirn sleeve that is adaptable to manufacture on a continuous and low cost basis.
Several methods are known for indenting the external surface of thermoplastic tubes. One such method whereby indentations are made on the external surface of a pirn sleeve is described in U.S. Pat. No. 3,095,161 issued June 25, 1963 to R. Atwood and C. C. L'Allemand.
It is an object of the present invention to provide a novel method for indenting the external surface of a thermoplastic tube to make such a sleeve.
It is another object of the present invention to provide a novel method for indenting the external surface of a thermoplastic tube being continuously withdrawn from a source of supply.